Apparatus for preventing corrosion in oil wells



FIG.2

G. H. ROHRBACK Filed July 22, 1952 APPARATUS FOR PREVENTING CORROSION IN OIL WELLS FIG. 3

INVENTOR G/LSON H. ROHRBACK ATTORNEYS Sept. 13, 1955 APPTUS FOR PREVENTING CORROSION IN OIL WELLS Application July 22, 1952, Serial No. 3%,321

7 Claims. (Cl. 166243) My invention relates to apparatus for injecting material at the bottom of a well, andparticularly to apparatus for injecting corrosion inhibitors into an oil well.

Corrosion of ferrous metal surfaces in contact with the producing streams of oil wells has long beenrecognized as a serious operating problem by petroleum pro: ducers. to this problem, and severalmethods ofreducing corrosion rates and therefore reducing the frequency of replacement of well tubing, sucker rods and other subsurface apparatus, have been proposed.

Chemists have found a number of' compounds which satisfactorily retardcorrosion. Examples of these products are sodium hydroxide, sodium carbonate and sodium dichromate. of introducing these compounds into a well to effectively control corrosion have not been developed.- According to prior art teachings, of which I am' aware, liquid corrosion inhibitors or solutions of solid inhibitors have been introduced into the annulus of producing wells. The.

corrosion inhibitor then falls to the bottom of the well to protect the metal members from corrosion. This means of introducing corrosion inhibitor liquids is not applicable, however, to wells having a sealed-01f annulus. For wells in which the annular mode of introduction of corrosion inhibitor is impractical, corrosion inhibitor has been introduced directly to the tubing. However, pro.- duction must be interrupted periodically for the application of corrosion inhibitor according to this method'and' must not be resumed until the liquid has fallen to suflicient depth in the well so that it will contact. the entire.

length of tubing and thus give optimum corrosion protection.

reach the bottom of the well. Thus, it' is more probable that only the top portion of the tubing string will be protected.

The corrosion problem is of sufiicient severity that such time-consuming corrosion inhibiting practices are followed in some wells. to a lesser extent tothe corrosion problem, the expense.

of the use of present corrosion inhibitors is too great.

economically to justify its use. In these cases corrosion of the well equipment is acceptedas the lesser of the two evils.

My invention provides an inexpensive methodof'using corrosion inhibitor liquids.

It is an object of my invention to provide apparatus for injecting corrosion inhibitor liquids into producing.

of corrosion inhibitor liquids are commerciallyavailable- Considerable research efiort has been directed.

However, completely satisfactory methods.

Furthermore, there is no assurance that liquid. inhibitor introduced at the top of the tubing string will' In other wells which are subject.

Patent J. orthe electrical cables running through the annulus.

.;- injected; at the rate of 0.14 cc. per minute.

well at relatively infrequent intervals of the order of' one. year.

It is important to the concept of my invention that the injection system be one which is compatible with.

the present types of well equipment. It is preferable that the injector have a maximum diameter no larger than the tubing collars of the well. itshould be no longer than 50 feet, and preferably no longer than feet. It must have mechanical characteristics such that it need not be serviced during the time in which it is dispensing one charge of corrosion inhibitor. For convenience of use, it mustbe self-contained.in the sense that it must not be connected to the pumping rod If the length of'the injector is not'to exceed 40 feet and is to fitwithin the collar of a 2 /2 inch well tube, it would contain approximately4500 cubic inches. If the inhibitor is to be played out over a period of a year, it must be Or stated differently, if a water solution of the well-known inhibitor compound sodium chromate (NazCrO4-2H2O) wereplayedout continuously for a period of' six months, the inhibitor concentration would be 25 p. p. m. in a Wellproducing about barrels of water daily. Many wells have been treated-successfully for corrosion control with injection of sodium dichromate at rates,of about 25 p. p. m. active inhibitor.

Fora'liquid injector to be acceptable to well operating personnel andpraetical from an economic viewpoint, it must be so arranged that it requires a minimum of attention over an extended'period of time. have provided a metering system foruse with liquidcorrosion inhibitors.

Thenovel' features of' my invention are. set forth with more-particularity inthe accompanying claims. The. in-. vention itself; however, with respect to the details thereof; together with its additional objects and advantages, may be better understood from the following description of a specific embodiment'with reference. to the accompanying drawings, in which:

Figure 1 shows a dispenser according to oneembodiment of my invention.

Figure 2 shows a, modification of my invention for. use with a liquid-inhibitor which is proneto react with well gases.

Figure 3' shows a modification of my invention by which predetermined quantities of a liquidcorrosion inhibitor are meteredintermittently into the well fluid.

Figure 1 shows a continuous feeder for. maintaining a predetermined concentration of liquid inhibitor in the well fluidatthe bottom of the oil well. This apparatus comprises a section of tubing 5 which is attached to the bottom of the well tubingstring. The tubing string above the section 5 may include pump and a perforated section oftubing through which well fluid flows to the pump to be pumped to the surface of the well. The apparatus is equally applicable to a well which flows as a result of pressure on the liquids rather than by virtue of the action of a pump. It is customary to provide a length of tubing below the perforated section, through which passes the well effluent. This portion of the tubing is replaced by the tubing section 5. Thesection of tubing 5 has closure members 6 and 8 across its upper and lower portions to form a'reservoir 10 within which is stored a quantity of liquid corrosion inhibitor which is subsequently released into the bottom of the well in a manner to be described.

For convenience of use,

Accordingly, I.

A support arm 7 is located at an inclined angle below the tubing section in such a position that it lies outside of the reservoir 10 in a position to be exposed to well fluids. A copper plate 9 is aflixed to the upper surface of the support arm 7. A slender tube 11 is slidably mounted in an opening in the lower closure member 8 of the tubing section. A port 17 is formed through the wall of the tube 11 adjacent its upper end to provide a communication from the interior of the reservoir through the port and tube to the well fluid around the tubing section 5. When the port 17 is above the surface of the liquid inhibitor 19, no part of the inhibitor flows out. When the port 17 is below the surface of the liquid, at small quantity of corrosion inhibitor can flow into the well.

An 0 ring seal 13 forms a fluid-tight seal around the tube 11. The tube 11 is fitted in an axial position within the chamber and has a weight 15 bearing down on its upper end to bias the tube 11 downward. The tube 11 is constructed of magnesium. A vent tube 21 connects the well below the chamber to the air space above the level of the inhibitor. The vent tube 21 provides a means for equalizing pressures so that the pressure in the body of the inhibitor is the same as the well pressure. There is, then, no back flow of well fluid into the reservoir.

In operation, the tubing section 5 is lowered to the bottom of the well. The port 17 is above the surface of the inhibitor fluid, and the inhibitor fluid is unable to flow out of its confining chamber. The lower end of the magnesium tube 11 rests against the copper plate 9 on the support arm 7. magnesium tube in the area of contact between the copper and the magnesium. Corrosion takes place as the result of bimetallic contact in the presence of an electrolyte. The rate of corrosion of the magnesium, then, is independent of the nature of the fluid and is dependent solely upon the potential difference between the magnesium and the copper. Copper is termed the more noble metal after the terminology of classical science since the copper causes the magnesium to corrode. The magnesium is anodic with respect to copper, and it is the potential difference between the two metals which determines the rate of corrosion of the anodic element.

As the tube 11 corrodes, it is shortened and its port 17 slowly moves downward. When the drain port reaches the level of the liquid inhibitor, the liquid inhibitor begins to flow out through the hollow tube 11 into the well. The rate of flow of the inhibitor is dependent upon the rate at which the magnesium tube 11 dissolves. Gases from the well flow through the vent tube 21 to equalize pressure in the chamber containing the liquid inhibitor.

When inhibitors such as sodium siilcate are to be used in apparatus according to my invention, it is desirable to provide a means to prevent reaction of the inhibitor solution in the reservoir with well gases. The inhibitor sodium silicate solution is highly basic and would react with the carbon dioxide of the well gases which pass through the vent 21. The flow of well gases would cause the inhibitor solution to become acidic from carbon dioxide absorption, and silicic acid would precipitate. It has been found that sodium silicate will operate satisfactorily to inhibit corrosion despite the presence of well gases in Well fluids.

Accordingly, I have developed the apparatus shown in Figure 2 to overcome this difliculty. This apparatus is similar to that shown in Figure 1 except that the upper end of the tube 11 is formed with an inverted U shape, i. e., a portion of tubing extends upward at an oblique angle to contact the tubing 11 at its upper end. The tubing is opened at the lower end of its lateral branch. A layer of oil 36 lies on the surface of the inhibitor 19. The open end of the upper portion of the tube is positioned below the layer of oil so that it is submerged in the corrosion inhibitor in the reservoir. As the tube 11 moves downward, it passes inhibitor solution to the well fluid, but due to its U shape, it does not permit the oil Electrolytic action causes corrosion of a 4 36 to flow out of the chamber. The oil protects the inhibitor from contact with the well gases and thereby prevents reaction with the inhibitor.

It has been found that several types of inhibitors exhibit satisfactory corrosion inhibition properties when they are introduced, periodically in measured quantities. It is only necessary that a new batch of corrosion inhibitor fluid be introduced into the well fluid before the effect of the previous batch of inhibitor has subsided. The amount of inhibitor which must be introduced at one time and the frequency of introduction of the inhibitor is dependent upon the nature and the rate of flow of corrosive fluids within the well.

Figure 3 shows apparatus whereby corrosion inhibitors may be introduced into the well in predetermined quantities at regular intervals. A section of tubing such as the tubing 5, shown in Figure 1, has a top closure member 6 shown in Figure l and has a lower closure member 24 shown in Figure 3 to form a reservoir within which is stored a quantity of liquid corrosion inhibitor which is subsequently released into the well in a manner to be described. Below the reservoir 23 is a second reservoir 31 having a closure member 32. An opening in the closure members 24 and 32 is sealed around a valve rod 27 by an O ring seal. The rod is provided with notches at regularly spaced intervals. The vertical spacing between the O ring seals 29 and 33 is of a length which is not an integral multiple of the distance between two notched or necked-down sections on the rod 27. Thus, when a necked-down portion of the rod is opposite the 0 rin seal 29, a larger diameter portion of the rod is opposite the O ring seal 33. Fluid which is permitted to flow through the 0 ring seal 29 is then prevented from passing through the 0 ring seal 33. A vent tube 25 penetrates the closure member 24, communicating from the well external to the reservoir 23 to the space within the reservoir 23 above the surface of the liquid inhibitor. The rod 27 is constructed of magnesium and rests upon a copper support plate 35 which is rigidly affixed to the walls of the reservoirs in a manner not shown. The support for the copper plate 35 may be similar to the support 7 for the copper plate 9 shown in Figure l. A weight (not shown) may be placed at the top of the rod 27 to bias it downward against the copper plate 35. Under some circumstances it may be found that the weight of the rod 27 provides sufficient downward bias, and the weight may be omitted.

In operation, the chamber 23 is filled with inhibitor fluid, and the rod 27 is arranged to close the opening at the O ring seal. After the apparatus is placed at the bottom of a well, a bimetallic corrosion action of the contact between copper and magnesium causes the magnesium rod 27 to dissolve at its lower end. The magnesium rod 27 then is lowered by the effect of gravity as its lower end is corroded away, and the necl eddown portion falls Within the O ring seal 29. At this time, a larger diameter section of the rod 27 is within the 0 ring 33, and the lower chamber 31 is sealed off from the well fluid. Sufl'lcient inhibitor flows through the 0 ring seal 29 to fill the lower chamber 31. As corrosion of the magnesium rod continues, the O ring 2? is sealed off, and a small diameter portion on the magnesium rod 2"! fails opposite the O ring 33. The corrosion inhibitor in the chamber 31 then flows out to mix with the well fluid. After a predetermined interval, the magnesium rod further corrodes to close the lower 0 ring and open the O ring 29, and the process of introducing corrosion inhibitor to the well fluid is repeated.

The quantity of each batch of inhibitor is selected to be suflicient to provide corrosion protection during the entire time between the introduction of successive batches of inhibitor. In all of the embodiments of my invention herein described it is not essential that the moving element be constructed of magnesium and the supporting element of copper. It is only essential that the metals be so selected that one of them is corroded, and the eifective length of the moving element within the reservoir is decreased. This requirement is met if one of the elements is more noble than the other or one of them is more electro-positive.

Although I have shown and described a preferred embodiment of my invention, I realize that many modifications thereof are possible without departure from the spirit and scope of the invention. For example, my invention may be used to introduce materials other than corrosion inhibitor into an oil well. i do not intend, therefore, to limit my invention to the specific embodiment disclosed.

I claim:

1. A metering device for a liquid corrosion inhibitor comprising a reservoir for said liquid, a metallic element slidably mounted in a wall of said reservoir and biased to slide outwardly of said wall, support means stationarily aflixed to said reservoir and positioned outside of said reservoir to contact said element to restrain said elemert from sliding outwardly of said wall, said support means being formed of a metal more noble than said metallic element, means to produce deterioration of said metallic element where said metallic element contacts said support means to thereby permit said element to move outwardly of said wall, and means in said element to provide a passage for said liquid from within said reservoir to the exterior thereof.

2. A metering device for a liquid corrosion inhibitor comprising a reservoir for said liquid, a metallic element slidably mounted in a Wall of said reservoir and biased to slide outwardly of said wall, support means stationarily affixed to said reservoir and positioned outside of said reservoir to contact said element to restrain said element from sliding outwardly of said wall, said support means being formed of a metal cathodic to said metallic element to form a galvanic coupling within the less noble metal of said element and dissolving at the point of contact between said support means and said metallic element in the presence of well fluids, means to produce deterioration of said metallic element where said metallic element contacts said support means to thereby permit said element to move outwardly of said wall, and means in said element to provide a passage for said liquid from within said reservoir to the exterior thereof, said last-named means having a liquid-carrying capacity dependent upon the position of said metallic element relative to said wall.

3. A device for automatically dispensing a quantity of a liquid corrosion inhibitor into an oil well over a prolonged period of time comprising a reservoir for said inhibitor positioned in said well and substantially immersed in the fluids in said well, an elongated magnesium element positioned vertically in said reservoir and projecting through the bottom portion thereof in sliding relationship, a sealing means positioned between the said elongated magnesium element and the said bottom portion of said reservoir to prevent the said inhibitor from escaping from said reservoir, a copper element connected to said device and positioned outside of said reservoir in said fluids in said well and contacting the portion of said elongated magnesium element which projects from said reservoir to limit sliding movement of said elongated magnesium element through the said bottom portion of said reservoir, and means in said elongated magnesium element to provide a communicating passage between said reservoir and said oil well.

4. For use in admitting metered amounts of liquid into a well, the combination comprising a container for said liquid having an opening at its lower end, a metallic tube slidably disposed within said container, and extending through said opening, a fluid excluding seal in said opening adapted to permit vertical movement of said tube in said opening, a por in said tube within said container for allowing portions of the fluid in said container to flow from said container through said tube, a supporting plate of a metal cathodic to the metal in said tube, said supporting plate being secured to said container and disposed to support said tube by contacting the portion of said tube extending through said opening.

5. For use in admitting into a well containing electrolyte a first liquid which is disposed to react unfavorably when in contact with well gases, the combination comprising a closed container for said first liquid adapted to be placed at the bottom of said well, a vent tube extending through a wall of said container to a point inside said container above the level of said first liquid to equalize pressure within said container to that outside said container, a layer of a second liquid within said container having a lower specific gravity than said first liquid and which will not react unfavorably with said well gases and said first liquid, a vertical metallic tube in a vertical position in said container and extending through an opening in the bottom of the container, a fluid excluding seal in the opening adapted to permit vertical movement of the tube, a bent section at the upper end of said tube adapted to permit flow of fluid through said tube from a point below the second fluid, a supporting plate for said tube of a metal cathodic to the metal of said tube, said supporting plate being disposed to support said tube, said supporting plate being in the electrolytic environment at the point of its contact with the tube.

6. For use in injecting predetermined amounts of liquid at the bottom of a well, the combination comprising a container having two chambers, an opening in the bottom of each chamber, a fluid excluding seal in each opening, a vertical metal rod slidably disposed within said openings, the rod having portions of reduced external diameter at spaced points along its length, the portions being so disposed along said rod that they permit fluid flow through only one of said openings at a time, and a metal support for said rod external to said container, the metal of the support being cathodic to the metal of the rod.

7. For use in injecting a fluid into a well, comprising in combination a chamber for holding said fluid, a metal outlet tube slidably mounted in said chamber and having an outlet port in said chamber communicating with an opening outside said chamber in said well, a metal projection on said chamber adapted to support said tube, the metal of said surface being cathodic to the metal of said tube, whereby corrosion of said tube at said surface causes said outlet port to be lowered into said fluid.

References Cited in the file of this patent UNITED STATES PATENTS Re. 23,583 Eilerts Nov. 18, 1952 1,613,461 Johnson Jan. 4, 1927 1,873,084 Walker Aug. 23, 1932 2,401,546 Brown June 4, 1946 2,437,475 Oxford Mar. 9, 1948 

1. A METERING DEVICE FOR A LIQUID CORROSION INHIBITOR COMPRISING A RESERVOIR FOR SAID LIQUID, A METALLIC ELEMENT SLIDABLY MOUNTED IN A WALL OF SAID RESERVOIR AND BIASED TO SLIDE OUTWARDLY OF SAID WALL, SUPPORT MEANS STATIONARILY AFFIXED TO SAID RESERVOIR AND POSITIONED OUTSIDE OF SAID RESERVOIR TO CONTACT SAID ELEMENT TO RESTRAIN SAID ELEMENT FROM SLIDING OUTWARDLY OF SAID WALL, SAID SUPPORT MEANS BEING FORMED OF A METAL MORE NOBLE THAN SAID METALLIC ELEMENT, MEANS TO PRODUCE DETERIORATION OF SAID METALLIC ELEMENT WHERE SAID METALLIC ELEMENT CONTACTS SAID SUPPORT MEANS TO THEREBY PERMIT SAID ELEMENT TO MOVE OUTWARDLY OF SAID WALL, AND MEANS IN SAID ELEMENT TO PROVIDE A PASSAGE FOR SAID LIQUID FROM WITHIN SAID RESERVOIR TO THE EXTERIOR THEREOF. 